Corruption on the U.S. side of the Mexican border rose sharply in recent years as drug cartels targeted border agents as part of illicit drug and human trafficking, senior Obama administration officials told a Senate hearing on Thursday.

Customs and Border Protection (CBP) Commission Alan Bersin said the overwhelming majority of border patrol officers and agents are honest, “but the reality is that CBP employees have been and will continue to be targeted by criminal organizations or may otherwise seek to exploit their position of public trust for illicit gain. …”

“Gangs such as Los Zetas are becoming involved increasingly in systematic corruption to further alien and drug smuggling, including smuggling of aliens from designated special-interest countries likely to export terrorism,” Mr. Edwards said.

The two appeared at a hearing Thursday of the Homeland Security and Governmental Affairs subcommittee on disaster recovery and intergovernmental affairs.

Over the past six years, 127 CBP agents were arrested or indicted for corruption, the officials testified. Investigations of additional complaints rose to more than 4,500 cases last year.

Thursday’s hearing focused on the increase in these cases and the need for greater cooperation between the DHS inspector general and CPB, which in the past have not closely cooperated.

“As we continue to see successes in our efforts to secure our nation’s borders, our adversaries continue to grow more desperate in their attempts to smuggle humans and illegal contraband into this country,” Mr. Bersin said. “Our most valuable — as well as in some rare cases our most vulnerable — resources are our employees.”

The issue of corruption has slowly come to light in recent years as a result of several high-profile cases of U.S. officers who were caught helping cartels smuggle illegal contraband and humans across the border.

Last year one CPB officer, Martha Garnica, was sentenced to 20 years in prison after a sting operation showed her involvement with a Mexican crime syndicate called La Linea. And her story was not an isolated case.

Also in 2010, the inspector general opened 870 investigations related to CPB employees, a 48 percent increase from the previous year’s 595 cases. The cases included investigations into CBP employee corruption, civil rights abuses, and suspicious activity, Mr. Edwards said.

As a result, Congress passed the Anti-Corruption Border Act last year to put measures in place that would check new employees’ integrity. Under the act, the CBP must run background checks and polygraph tests on every new employee. So far, the organization has a backlog of 15,197 cases that need to be completed. Mr. Bersin said the CBP was on track to catch up with all cases by 2013.

Initial results were a cause for concern, Mr. Edwards said, noting that recent polygraph tests showed that up to 60 percent of CBP employees showed deception when asked questions about having a criminal record.

The Department of Homeland Security has struggled with targeting corruption because of confusion within its organizational structure. The 1978 Inspector General Act gave the inspector general authority for holding the agency accountable.

Mr. Bersin said the confusion often led to “outright confrontation” between CPB and the IG office.

Under Homeland Security Secretary Janet A. Napolitano, relations between the two offices improved, but both Mr. Edwards and Mr. Bersin said more work remains.